In various technical fields, CRTs (Cathode Ray Tubes) have gradually been replaced by hold-type display apparatuses including a liquid crystal display module or an EL display module.
It is considered, however, that hold-type display apparatuses are inferior in moving image qualities to impulse-type display apparatuses such as CRTs (Cathode Ray Tubes) in which a turn-on time during which an image is displayed and a turn-off time during which an image is not displayed are alternated.
That is to say, in a typical hold-type display apparatus, a whole one frame period is an image turn-on time. On this account, once a frame image is updated, an object is being displayed until the image is updated in the next frame, and the image displayed in this way appears as motion blur for the viewer.
To achieve improvement in the moving image quality as one of the objectives, various methods have been proposed to perform the driving in such a way as to time-divide a single frame for displaying one image into plural sub frames. An example of such methods is disclosed by Patent Document 1. It is noted that image display apparatuses adopting organic LED panels have been arranged so that vertical scanning is multiplexed.
In addition to the motion blur, liquid crystal display apparatuses have a typical problem of low response speed of liquid crystal elements. Because of this problem of response speed, liquid crystal display apparatuses have the following disadvantage: when input grayscales greatly change between successive frames, the brightness response level in the later frame may not reach a desired brightness level, i.e. may not reach the brightness level when input grayscales do not change between successive frames.
To compensate the low response speed, there is a known technology termed overshoot driving. Overshoot driving is arranged such that, in accordance with a change (increase or decrease) in input grayscales between successive frames, a voltage which is higher or lower than a voltage by which a desired grayscale level is achieved when input grayscales do not change between successive frames is supplied to liquid crystal elements, so that the liquid crystal elements are forcibly driven at a high speed. For example, Patent Document 2 discloses a technology to perform overshoot driving in a liquid crystal display apparatus in which a single frame is divided into plural sub frames (fields) for image display.
[Patent Document 1]
Japanese Laid-Open Patent Application No. 2005-173573 (published on Jun. 30, 2005)
[Patent Document 2]
Japanese Laid-Open Patent Application No. 2001-343956 (published on Dec. 14, 2001)